Transmission concern on 3/4 Chevy Suburban

Tranny is a L480E. Suburban is a 3/4 ton (2500) 4x4. 111,500 miles on it. Bought vehicle with 50,000 on it and no knowledge of history. Tranny had fluid & filter change 20,000 miles ago (not flushed). Now have an intermittant problem of 1,2,3rd gear won't shift immediately (takes a couple seconds & then shifts into gear). Want to flush fluid but I get conflicting information....flush, don't flush....due to unknowm history & mileage. Supposedly, if I flush, I run risk of dislodging accumulated 'crud' in tranny thus shortening life before a rebuild is required. Fluid at this point is brown & has a 'clutch' odor to it. The other day, when shifting into Drive, RPM's had to be increased dramatically to even get the vehicle to move (even people outside of vehicle asked me if I was trying to drive with the parking brake on!)......now it operates normally in all gears. Personal analysis is that I should flush now & take chance that it will at least provide new lubrication....I still think that it is just a matter of time before I will need to do a rebuild. If I only do a change then I am not really performing much benefit to the tranny....sort of like pouring pure water into a algea pond; no matter how much pure water I pour into the pond, it will still be contaminated. Does anyone have any advice to offer on which way to go? Should I just proceed forward with a rebuild now or just change fluid? Should I flush it or just drop pan? Here are pictures of new fluid next to fluid from the dipstick.

Welcome to the club. I don't care for trans flushes. I would drop the pan and look in the bottom of the pan. If theres nothing bad in the pan I would install new filter and when you fill trans I would add some Lucas transmission additive to the fluid. This stuff works well if you have a valve sticking in the trans. If you find alot of clutch pieces than it most likely time for a remanufacture.

Thank you for your experienced input. If I don't flush, would I just be mixing the couple of quarts of new fluid with cantaminated fluid that is in torque converter? How do I pull out more contaminated fluid without a flush other than what is in the pan?

Well what I do is run mine with fresh fluid for about a day and then I change the fluid again. I know its a pain but I've heard to many problems with the trans flushings. Maybe look into installing a new trans pan with a drain plug, thats what I did with my first trans service.